Device for treating vulnerable plaque

ABSTRACT

A method of treating vulnerable plaque comprising intentionally damaging or rupturing the vulnerable plaque using a wingless balloon which is inflated from a wingless unexpanded diameter to a limited expanded diameter. This process produces significant increase in ECM synthesis at the site of the damage or rupture. As a result, the method strengthens the vulnerable plaque while minimizing or avoiding damage to the surrounding wall of the body lumen or damaging a stable plaque mistakenly believed to be a vulnerable plaque. The method of the invention is particularly useful in treating a fibroatheroma type of vulnerable plaque. In one embodiment, the balloon is self-limiting such that it expands compliantly at initial inflation pressures, and above nominal pressure it expands noncompliantly. In an alternative embodiment, the balloon is inflated using a diameter-limiting device, such as a device which limits the inflation pressure or the volume of inflation fluid in the balloon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. patent applicationSer. No. 11/140,240, filed May 26, 2005, which is a divisional of U.S.patent application Ser. No. 10/032,322 filed Dec. 21, 2001, each of thedisclosures of which are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

This invention generally relates to treatment of atherosclerotic plaque,and particularly to treatment of vulnerable plaque using a ballooncatheter.

Percutaneous transluminal coronary angioplasty (PTCA) is a widely usedprocedure for treating the occlusion of coronary vessels byatherosclerotic plaque. In PTCA procedures, a guiding catheter isadvanced until the distal tip of the guiding catheter is seated in theostium of a desired coronary artery. A guidewire, positioned within aninner lumen of a dilatation catheter, is first advanced out of thedistal end of the guiding catheter into the patient's coronary arteryuntil the distal end of the guidewire crosses a lesion to be dilated.Then the dilatation catheter having an inflatable balloon on the distalportion thereof is advanced into the patient's coronary anatomy, overthe previously introduced guidewire, until the balloon of the dilatationcatheter is properly positioned across the lesion. Once properlypositioned, the dilatation balloon is inflated with fluid one or moretimes to a predetermined size at relatively high pressures (e.g. greaterthan 8 atmospheres) so that the stenosis is compressed against thearterial wall and the wall expanded to open up the passageway.Generally, the inflated diameter of the balloon is approximately thesame diameter as the native diameter of the body lumen being dilated soas to complete the dilatation but not overexpand the artery wall.Substantial, uncontrolled expansion of the balloon against the vesselwall can cause trauma to the vessel wall. After the balloon is finallydeflated, blood flow resumes through the dilated vessel and thedilatation catheter can be removed therefrom. In such angioplastyprocedures, there may be restenosis of the vessel, i.e. reformation ofthe arterial blockage from significant neointimal thickening relative tothe vessel diameter, which necessitates either another angioplastyprocedure, or some other method of repairing or strengthening thedilated area. To reduce the restenosis rate and to strengthen thedilated area, physicians frequently implant a stent inside the artery atthe site of the lesion. Studies have shown correlations between vesseldamage caused by PTCA and neointimal growth. See Schwartz et al., JACC,Vol. 19, No. 2: 267-74 (1992), incorporated by reference herein in itsentirety.

In the design of catheter balloons, characteristics such as strength,compliance, and profile of the balloon are carefully tailored dependingon the desired use of the balloon catheter, and the balloon material andmanufacturing procedure are chosen to provide the desired ballooncharacteristics. A variety of polymeric materials are conventionallyused in making catheter balloons. Use of polymeric materials such aspolyethyleneterephthalate (PET) that do not stretch appreciablyconsequently necessitates that the balloon is first formed by blowmolding, and then the deflated balloon material, in the form of deflatedwings, are folded around the catheter shaft prior to introduction of theballoon into the patient's body lumen. However, it can be desirable toemploy balloons that do not have deflated folded wings, but whichinstead can be expanded to the working diameter within the patient'sbody lumen from an essentially wingless, cylindrical or tubular shapewhich conforms to the catheter shaft. For example, catheter balloonshave been described which are formed of expanded polytetrafluoroethylene(ePTFE) expanded in place within the patient's body lumen withoutblow-molding the ePTFE tubing. The ePTFE tubing is formed of a sheet ofePTFE wrapped on a mandrel and then heated to fuse the layers of wrappedmaterial together, and the resulting tubular ePTFE balloon is bonded toa catheter-shaft.

A current therapeutic challenge is the treatment of unstable orvulnerable plaque. The term “vulnerable plaque” refers to anatherosclerotic plaque which may rupture and/or erode, with subsequentthrombosis, typically leading to acute myocardial infarction. In“stable” plaque, the lipid core or necrotic core is protected by arobust fibrous cap composed primarily of long chain extracellular matrixproteins (ECM) such as elastin and collagen. The strength of the fibrouscap is determined largely by ECM density, and especially the density ofcollagen. Various morphologic features have been associated withvulnerable plaque including thinned or eroded fibrous caps, lesioneccentricity, proximity of constituents having very different structuralmoduli, e.g., lipid and fibrous tissue, and the consistency anddistribution of lipid accumulations. The most common type of vulnerableplaque, often called fibroatheroma, is a raised plaque beneath theinnermost arterial layer (i.e., the intima), containing a large lipidcore or a large necrotic core rich in lipids, cholesterol crystals,cholesterol esters, macrophages, and other cells, and having a fibrouscap which can become weakened. When ruptured, the luminal blood becomesexposed to highly thrombogenic core material, such as tissue factor(TF), which can result in total thrombotic occlusion of the artery. Dueto the substantial danger posed by vulnerable plaque, it would be asignificant advance to provide a method of treating such lesions.

SUMMARY OF THE INVENTION

This invention is directed to a method of treating vulnerable plaque,comprising intentionally damaging or rupturing the vulnerable plaqueusing a wingless balloon which is inflated from a wingless unexpandeddiameter to a limited expanded diameter. This process producessignificant increase in extracellular matrix protein (ECM) synthesis atthe site of the damage or rupture. As a result, the method strengthensthe vulnerable plaque while minimizing or avoiding damage to thesurrounding wall of the body lumen or to a stable plaque mistakenlybelieved to be a vulnerable plaque. The method of the invention isparticularly useful in treating a fibroatheroma type of vulnerableplaque, although the method is useful in treating any of the types oflesions considered within the class of vulnerable plaque. The method ofthe invention generally comprises positioning a wingless balloon of aballoon catheter in a portion of a body lumen having a vulnerableplaque, or having a lesion believed to be a vulnerable plaque, andinflating the wingless balloon. The balloon is inflated from a winglessunexpanded diameter to an expanded diameter into contact with a walldefining the portion of the body lumen having the vulnerable plaque, tothereby intentionally damage or rupture the vulnerable plaque.

The balloon is expanded into contact with the vulnerable plaque tocompress the vulnerable plaque. The compression damages or ruptures thefibrous cap of the vulnerable plaque. Damaging the fibrous cap producessome disruption which is not a total cap rupture, such as some form ofendothelial denudation, partial fracturing in the cap typically nearestthe lumen, and the like. Thus, the term “damage” should be understood toinclude some form of modification, which induces extracellular matrixsynthesis. Rupturing the fibrous cap completely breaks through at leasta section of the cap, and thus can allow the entities contained in thelipid or necrotic core of the vulnerable plaque to be released throughthe cap opening. Consequently, in one embodiment, the method of theinvention includes treating the patient with antithrombotic agentsduring compression of the vulnerable plaque. The damage or rupture tothe vulnerable plaque is designed to induce extracellular matrixsynthesis and thus increase the extracellular matrix density, therebyincreasing the strength of the fibrous cap. The stronger fibrous capstabilizes the plaque if vulnerable and decreases the risk that avulnerable plaque will cause thrombotic occlusion.

The term “wingless” should be understood to refer to a balloon whichdoes not have deflated wings folded around the balloon to form a lowprofile configuration for insertion and advancement of the catheter inthe body lumen. Thus, the wingless balloon has little or no wings,unlike catheter balloons which deflate from a blow-molded expandeddiameter to form wings. Due to the lack of deflated wings prior toinflation of the balloon in the body lumen, the balloon can be inflatedto a working diameter at low pressures to uniformly expand against thevulnerable plaque, and without requiring wings to unfold as the ballooninflates. The wingless balloon expands uniformly to minimize shearloading on the plaque and wall upon inflation, thus preventing orinhibiting dissection in the vessel normal wall opposite the plaquewhich might otherwise occur.

The wingless balloon may be formed by a variety of conventional methods.For example, in one embodiment, the wingless balloon is formed by heatfusing a wrapped sheet of polymeric material to form a tubular balloonhaving a wingless unexpanded diameter which is secured to a cathetershaft. Alternatively, depending on the balloon material, the winglessballoon can be formed by heat-shrinking a blow-molded balloon to shrinkthe balloon to a wingless unexpanded diameter, which is particularlysuitable for forming a wingless balloon from a radiation crosslinkedpolyolefin.

The balloon has a nominal diameter about equal to the inner diameter ofthe vessel at the site of the vulnerable plaque, so that the balloon ischosen, depending on the diameter of the vulnerable plaque, to expandinto contact with the plaque to damage or rupture the plaque withoutover expanding the vessel. The desired outer diameter of the inflatedballoon depends on the size of the body lumen at the vulnerable plaqueand the nature of the vulnerable plaque. In a presently preferredembodiment, the outer diameter of the inflated balloon is about 1.5 toabout 10 mm, preferably about 2 to about 6 mm, and most specifically, istypically about 2.5 to about 5 mm.

In a presently preferred embodiment, the balloon expands in aself-limiting manner, so that the balloon expands at low pressures tothe working diameter and thereafter expands very little. In a presentlypreferred embodiment, the self-limiting balloon has at least a firstlayer formed of a polymeric material selected from the group consistingof expanded polytetrafluoroethylene (ePTFE), and ultra high molecularweight polyolefins, which may be an expanded ultrahigh molecular weightpolyolefin. A presently preferred ultra high molecular weight polyolefinis ultra high molecular weight polyethylene. The porous ePTFE or ultrahigh molecular weight polyolefin balloon typically has a second layer ofa different material. In one embodiment, the second layer is formed of amaterial such as a polyurethane elastomer.

Preferably, in the embodiment in which the wingless balloon is aself-limiting balloon (e.g., ePTFE or ultrahigh molecular weightpolyolefin balloon), the balloon has a highly compliant radial expansionwithin a first inflation pressure range, and is noncompliant within asecond, higher inflation pressure range. For example, in one embodiment,the self-limiting, wingless balloon has a compliance curve such that theouter diameter increases by about 100% to about 400% of the uninflateddiameter at an inflation pressure of up to about 10 atm, and thereafterincreases by about 2% to about 15% of nominal at an inflation pressurewithin a second, higher inflation pressure range of about 10 atm toabout 20 atm. Thus, the diameter at a given pressure increases quicklyat a first rate up to the nominal diameter at the nominal pressure, andthen sharply changes to a second low rate of increase at higherinflation pressures. The nominal pressure required to expand theself-limiting balloon to the nominal diameter, and at which the balloonradial expansion changes from compliant to noncompliant, may range fromabout 4 atm to about 12 atm, and is typically about 10 atm to about 12atm, depending on the characteristics of the balloon. In the method ofthe invention, the self-limiting, wingless balloon is typically inflatedat an inflation pressure within the second, higher inflation pressurerange, to an expanded diameter at or above the nominal diameter, withoutexpanding the balloon significantly beyond the nominal diameter, tothereby damage or rupture the vulnerable plaque without overexpandingthe vessel. Consequently, the balloon expands to produce controlleddamage to the vulnerable plaque, in a manner atraumatic to thesurrounding tissue and with minimal consequence to a stable plaque.

In another embodiment, the balloon is inflated using a diameter-limitingdevice, such as a device which limits the inflation pressure or thevolume of inflation fluid in the balloon. Pressure-limiting devicesinclude a pressure relief valve in fluid communication with theinflation lumen of the balloon catheter. In a presently preferredembodiment, the pressure relief valve limits the inflation pressure inthe balloon to about 4 to about 20, preferably about 4 to about 14 atm,and most preferably to about 4 to about 10 atm. The pressure or volumeof the inflation fluid required to inflate the balloon to the desireddiameter depends on a variety of factors including the compliance of theballoon, the resistance from the lesion, and the stenosis degree (i.e.,extent of occlusion in the lumen). In the embodiment using adiameter-limiting device to inflate the balloon, the balloon can beformed of a variety of suitable materials, such as polyurethaneelastomers, polyurethane copolymers such as silicone polyurethanes,segmented polyamide block copolymers, and segmented polyester blockcopolymers, styrene butadiene rubber or derivatives, and radiationcrosslinked polyolefinic elastomers. A balloon formed of these materialstypically expands compliantly at the inflation pressures used in themethod of the invention, so that the pressure-limiting device results ina low pressure inflation which limits the expanded diameter of theballoon to control the effect on the body lumen from the balloonexpansion. For example, in one embodiment, the compliant ballooninflated with a diameter-limiting device expands by about 40% to about400% of the uninflated diameter at an inflation pressure of about 4 toabout 10 atm. Thus, in one embodiment, the pressure-limiting devicelimits the inflation pressure to about 4 to about 10 atm.

By inflating the wingless balloon using a diameter-limiting device or byusing a self-limiting balloon, the method of the invention provides forcontrolled damage or rupture of the vulnerable plaque and is atraumaticto the healthy wall of the surrounding body lumen. The balloon has anexpanded configuration at the working pressure (i.e., the inflationpressure used to expand the balloon into contact with the vulnerableplaque) which is sized such that the balloon does not over expand thehealthy wall of the surrounding body lumen. For example, the balloondoes not radially over expand or increase in length axially duringinflation. Such over expansion of the healthy vessel wall could lead todissection or occlusion of the body lumen, as for example, by yieldingthrombosis or inducing smooth muscle cell neointimal proliferation inthe healthy vessel wall. The vulnerable plaque may be eccentricallydisposed in the body lumen. In one embodiment, the expanded diameter ofthe balloon working length is about equal to the inner diameter of bodylumen at the location of the vulnerable plaque, so that the inflatedballoon does not over expand the healthy vessel wall opposite aneccentric vulnerable plaque In one embodiment, the inflated balloon hasa working length which is not longer than the vulnerable plaque, so thatthe balloon does not expand the healthy vessel wall on either end of thevulnerable plaque. However, in another embodiment, and particularly theembodiment having a self-limiting balloon which inflates to a controlledand limited diameter with increasing pressure, the balloon workinglength is longer than the vulnerable plaque. In one embodiment, theballoon working length expanded diameter is about equal to or less thanthe inner diameter of the body lumen located longitudinally adjacent tothe vulnerable plaque, so that the expanded balloon may contact but doesnot over expand the healthy body lumen wall on either end of thevulnerable plaque. Additionally, stable, fibrotic lesions would beminimally affected by the low pressure, limited-diameter dilatation inaccordance with the method of the invention. Therefore, treating plaquesincorrectly believed to be vulnerable should be a benign process withthe method of the invention.

The method of the invention provides for treatment of vulnerable plaqueby intentionally damaging or rupturing the vulnerable plaque to therebyproduce a stronger fibrous cap around the core of the plaque. Inflatinga wingless balloon to a limited expanded diameter damages the vulnerableplaque without damaging the surrounding healthy vessel wall or a stablelesion. The balloon has an initial wingless profile prior to inflationin the body lumen, and inflates to the working diameter at lowpressures, preferably with little or no change in compliance behaviorwith multiple, low pressure inflation-deflation cycles. These and otheradvantages will become more apparent from the following detaileddescription and exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a ballooncatheter useful in a method embodying features of the invention, withina body lumen at the site of an eccentric vulnerable plaque.

FIG. 2 is a transverse cross sectional view of the balloon cathetershown in FIG. 1, taken along line 2-2.

FIG. 3 is a transverse cross sectional view of the balloon cathetershown in FIG. 1, taken along line 3-3.

FIG. 4 illustrates the balloon of FIG. 1 inflated at the workingpressure to an expanded diameter in contact with the vulnerable plaque.

FIG. 5 is a transverse cross sectional view of the inflated balloonexpanded into contact with the vulnerable plaque in the body lumen shownin FIG. 4, taken along line 5-5 of FIG. 4.

FIG. 6 is a transverse cross sectional view of the vulnerable plaque inthe body lumen shown in FIG. 5, after the balloon is deflated andremoved from the body lumen.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an over-the-wire type balloon catheter 10, such as anangioplasty catheter, useful in a method of treating vulnerable plaquewhich embodies features of the invention. Catheter 10 generallycomprises an elongated catheter shaft 12 having an outer tubular member14 and an inner tubular member 16. Inner tubular member 16 defines aguidewire lumen 18 (FIG. 2) configured to slidingly receive a guidewire20. The coaxial relationship between outer tubular member 14 and innertubular member 16 defines annular inflation lumen 22. An inflatableballoon 24 disposed on a distal section of catheter shaft 12 has aproximal skirt section 25 sealingly secured to the distal end of outertubular member 14 and a distal skirt section 26 sealingly secured to thedistal end of inner tubular member 16, so that its interior 27 is influid communication with inflation lumen 22. An adapter 30 at theproximal end of catheter shaft 12 is configured to provide access toguidewire lumen 18, and to direct inflation fluid through arm 31 intoinflation lumen 22. In the embodiment illustrated in FIG. 1, theuninflated balloon 24 has a wingless, low profile configuration prior toinflation. FIGS. 2 and 3 illustrate transverse cross sectional views ofthe distal end of the catheter shown in FIG. 1, taken along lines 2-2and 3-3, respectively.

In FIG. 1, the balloon 24 is illustrated in a low profile, winglessunexpanded configuration for introduction and advancement within thebody lumen 34. Balloon 24 is inflated by introducing inflation fluidinto the inflation lumen 22 from arm 31 of proximal adapter 30. In theembodiment of FIG. 1, catheter 10 has a pressure relief valve 32 withinthe adapter 30, which, in one embodiment, limits the pressure within theballoon to thereby limit the expanded diameter of the inflated balloon24.

FIG. 1 illustrates the catheter 10 with balloon 24 positioned in aportion of a body lumen 34 defined by a wall 35 having a vulnerableplaque 36. The vulnerable plaque 36 has a lipid or necrotic core 37surrounded by a thin fibrous cap 38. As best illustrated in FIG. 3, thevessel wall 35 has a medial layer 39 surrounding an intimal layer 40,and vulnerable plaque 36 is within the intimal layer 40. For ease ofillustration, medial and intimal layers 39 and 40 of wall 35 are notseparately illustrated in FIG. 1.

In accordance with a method of the invention, the balloon 24 ispositioned at the site of vulnerable plaque 36 and the balloon 24 isinflated to expand the balloon from a wingless unexpanded diameter to anexpanded diameter, to intentionally damage or rupture the vulnerableplaque. The vulnerable plaque can be identified using a variety ofmethods which have been suggested in the field such as intravascularimaging, spectroscopic measurement, and using temperature sensors tomeasure the elevated temperature gradients of the vulnerable plaque. Itshould be understood that the method of the invention is useful intreating lesions believed to be vulnerable plaque, and does not requiredabsolute identification of the plaque as a vulnerable plaque fortreatment, and expansion of the balloon in accordance with the method ofthe invention at the site of stable plaque incorrectly believed to bevulnerable is preferably a benign process. Prior to expanding theballoon to compress the vulnerable plaque, the physician typicallydetermines the diameter of the portion of the body lumen having thevulnerable plaque 36, using conventional imaging methods such asquantitative angiography, ultrasonic or magnetic resonance imaging, oroptical coherence tomography (OCT). The physician then chooses theappropriate balloon-to-vessel diameter, and expands the balloon to thatpreselected diameter which corresponds to the diameter of the portion ofthe body lumen having the vulnerable plaque 36. FIG. 4 illustratesballoon 24 inflated at the working pressure to an expanded diameter incontact with the portion of the wall 35 having vulnerable plaque 36. Theballoon is expanded to a diameter sufficient to compress the vulnerableplaque 36. FIG. 5 illustrates a transverse cross section of the expandedballoon shown in FIG. 4, expanded to compress the vulnerable plaque 36,forming rupture 42. Due to the expansion of the balloon 24 to acontrolled, limited diameter, balloon 24 expands into contact with thewall 35 of the body lumen 34 at the site of the vulnerable plaquewithout damaging the wall 35 adjacent to the vulnerable plaque. Thus,the portions of the wall 35 opposite to and on either end of theeccentric vulnerable plaque 36 of FIG. 1 are not over expanded anddamaged by the balloon 24.

FIG. 6 illustrates a transverse cross sectional view of the body lumen34 after the vulnerable plaque 36 is ruptured by the expansion of theballoon 24 illustrated in FIG. 4, directly after deflation of theballoon 24. Antithrombotic agents such as heparin are preferablyadministered during or before the expansion of balloon 24, so thatthrombosis caused by the damage or rupture to the vulnerable plaque 36is limited or avoided. For example, an antithrombotic agent can bedelivered to the body lumen 34 through the guiding catheter (not shown)and/or through the lumen 18 of the inner tubular member 16.Alternatively, an antithrombotic agent can be incorporated in a porouslayer (e.g., ePTFE layer) of the balloon 24 and released therefrom whenthe balloon is inflated. Damaging or rupturing the vulnerable plaque 36will induce extracellular matrix synthesis to thereby increase thestrength of the fibrous cap 38 and reduce the risk of rupture of theplaque 36 in an uncontrolled manner.

In a presently preferred embodiment, balloon 24 is a self-limitingballoon which expands to a limited, controlled diameter. In oneembodiment, the self-limiting balloon 24 has at least one layer formedof a porous material such as ePTFE or ultrahigh molecular weightpolyethylene. In one embodiment, the ePTFE or ultra high molecularweight polyethylene polymers have a node and fibril microstructure, andare generally not melt extrudable into tubular form. The node and fibrilmicrostructure is produced in the material using conventional methods inwhich the material is heated, compacted, and stretched. Thus, in oneembodiment, the balloon comprises a polymer having a node and fibrilmicrostructure. The ePTFE or ultrahigh molecular weight polyethyleneballoon 24 typically has a nonporous second layer. For ease ofillustration, multiple layers are not illustrated in balloon 24. In oneembodiment, the ePTFE or ultrahigh molecular weight polyethylene balloon24 has a first layer formed of ePTFE or ultrahigh molecular weightpolyethylene, respectively, and a second layer formed of an elastomericmaterial, including polyurethane elastomers, silicone rubbers,styrene-butadiene-styrene block copolymers, and segmented polyamideblock copolymers, and the like. The elastomeric second layer isgenerally on the interior of balloon, although in other embodiments itmay be on the exterior of the balloon. The elastomeric second layerlimits or prevents leakage of inflation fluid through the microporousePTFE or ultrahigh molecular weight polyethylene to allow for inflationof the balloon, and expands elastically to facilitate deflation of theballoon to a low profile deflated configuration. The elastomericmaterial forming the second layer may consist of a separate layer whichneither fills the pores nor disturbs the node and fibril structure ofthe ePTFE or ultrahigh molecular weight polyethylene first layer, or itmay at least partially fill the pores of the first layer. The ePTFE orultrahigh molecular weight polyethylene layer is typically formed byheat fusing wrapped layers of the material together to form the firstlayer of the balloon.

Preferably, in the embodiment having a self-limiting balloon, balloon 24has a high compliance within a first inflation pressure range, and lowcompliance at higher inflation pressures above the pressure required toreach the nominal diameter of the balloon. For example, self-limitingballoon 24 may expand compliantly within a first inflation pressurerange up to about 10 atm, and expand with a low compliance of about 0.01to about 0.015 mm/atm within the second, higher inflation pressure rangeof about 10 to about 20 atm, more specifically about 10 to about 14 atm.The pressure ranges of the self-limiting balloon will vary depending oncharacteristics of the balloon, and the second pressure range, withinwhich the balloon is noncompliant, may be about 4 to about 14 atm, orabout 10 to about 20 atm. Although illustrated in the embodiment of FIG.1, pressure relief valve 32 is typically not used in the embodimenthaving a self-limiting balloon. In one embodiment, the balloon isinflated within the second pressure range at the site of the vulnerableplaque 36, to an expanded diameter not more than about 2% to about 15%greater than the nominal diameter of the balloon.

In an alternative embodiment, balloon 24 is inflated using adiameter-limiting device, such as pressure relief valve 32. Preferably,the balloon 24 is highly compliant in the embodiment using the pressurerelief valve 32. For example, the highly compliant balloon expands tothe working expanded diameter at a compliance rate of about 0.04 toabout 0.05 mm/atm over the inflation pressure range of about 4 to about10 atm. Such highly compliant balloon materials include polyurethanesincluding polyurethane elastomers, silicone styrene elastomers such asC-Flex available from Concept Polymers, styrene butadiene rubber orderivative, segmented polyamide or polyester block copolymers, andradiation crosslinked polyolefinic elastomers. A presently preferredcompliant balloon material is a polyurethane elastomer, such as anaromatic polyether polyurethane such as Tecothane 1065D having a Shoredurometer hardness of about 65D, available from Themedics. However, avariety of suitable grades of polyurethane can be used includingTecothane 1075D. A balloon formed of polyurethane is preferably formedby melt extruding the polyurethane to form a tubular body which issecured to catheter shaft. The polyurethane tubular body is prestretchedor otherwise weakened, as for example by blow molding and heatshrinking, so that the balloon can be expanded in the body lumen fromthe low profile, wingless diameter.

The dimensions of catheter 10 are determined largely by the size of theballoon and guidewires to be employed, catheter type, and the size ofthe artery or other body lumen through which the catheter must pass orthe size of the stent being delivered. Typically, the outer tubularmember 14 has an outer diameter of about 0.025 to about 0.04 inch (0.064to 0.10 cm), usually about 0.037 inch (0.094 cm), the wall thickness ofthe outer tubular member 14 can vary from about 0.002 to about 0.008inch (0.0051 to 0.02 cm), typically about 0.003 to 0.005 inch (0.0076 to0.013 cm). The inner tubular member 16 typically has an inner diameterof about 0.01 to about 0.018 inch (0.025 to 0.046 cm), usually about0.016 inch (0.04 cm), and wall thickness of 0.004 to 0.008 inch (0.01 to0.02 cm). The overall length of the catheter 10 may range from about 100to about 150 cm, and is typically about 135 cm. Preferably, balloon 24may have a length about 0.5 cm to about 6 cm, and an inflated workingdiameter of about 3 to about 10 mm.

Inner tubular member 16 and outer tubular member 14 can be formed byconventional techniques, for example by extruding and necking materialsalready found useful in intravascular catheters such a polyethylene,polyvinyl chloride, polyesters, polyamides, polyimides, polyurethanes,and composite materials. The various components may be joined usingconventional bonding methods such as by fusion bonding or use ofadhesives. Although the shaft is illustrated as having an inner andouter tubular member, a variety of suitable shaft configurationsconventionally used in dilatation catheters may be used including a duallumen extruded shaft having a side-by-side lumens extruded therein.Similarly, although the embodiment illustrated in FIG. 1 isover-the-wire stent delivery catheter, balloons of this invention mayalso be used with other types of intravascular catheters, such as andrapid exchange dilatation catheters. Rapid exchange catheters generallycomprise a distal guidewire port in a distal end of the catheter and aproximal guidewire port distal of the proximal end of the shaft, andtypically spaced a substantial distance from the proximal end of thecatheter, and a short guidewire lumen extending between the proximal anddistal guidewire ports in a distal section of the catheter.

While the present invention is described herein in terms of certainpreferred embodiments, those skilled in the art will recognize thatvarious modifications and improvements may be made to the inventionwithout departing from the scope thereof. Moreover, although individualfeatures of one embodiment of the invention may be discussed herein orshown in the drawings of the one embodiment and not in otherembodiments, it should be apparent that individual features of oneembodiment may be combined with one or more features of anotherembodiment or features from a plurality of embodiments.

1. A device for treating vulnerable plaque, comprising a ballooncatheter having a wingless balloon with an unexpanded diameter whichinflates to an expanded diameter wherein such expanded diameter isselected to intentionally damage such plaque by disrupting a fibrous capwithout cap rupture, to thereby strengthen the vulnerable plaque byinducing extracellular matrix protein synthesis.
 2. The device of claim1, wherein said expanded diameter corresponds to the diameter of aportion of body lumen in which the vulnerable plaque is located, wherebythe vulnerable plaque can be damaged without damaging the body lumenwall adjacent to the vulnerable plaque.
 3. The device of claim 1,wherein said catheter is configured for delivering an antithromboticagent within the body lumen.
 4. The device of claim 1, wherein theballoon has a highly compliant radial expansion up to a nominal expandeddiameter within a first inflation pressure range, and a low compliantradial expansion within a second higher inflation pressure range.
 5. Thedevice of claim 4, wherein the balloon has at least one layer formed ofa polymeric material selected from the group consisting of expandedpolytetrafluoroethylene, and expanded ultrahigh molecular weightpolyolefin, and the balloon is inflated at an inflation pressure withinthe second higher inflation pressure range.
 6. The device of claim 5,wherein the balloon is inflated at an inflation pressure of about 10 atmto about 20 atm.
 7. The device of claim 5, wherein the at least onelayer of expanded polytetrafluoroethylene, and expanded ultrahighmolecular weight polyolefin is porous with an antithrombotic agentwithin the pores.
 8. The device of claim 4, wherein the balloon expandsto an expanded diameter of about 2% to about 15% greater than thenominal diameter within the second, higher inflation pressure range. 9.The device of claim 1, further comprising a diameter-limiting inflationdevice.
 10. The device of claim 9, wherein the diameter-limiting devicecomprises a pressure relief valve within a proximal adapter of theballoon catheter, which limits the pressure in the balloon to about 4 toabout 10 atm.
 11. The device of claim 1, wherein the balloon isexpandable to a working, nominal outer diameter with a highly compliantradial expansion within a working pressure range of the balloon.
 12. Thedevice of claim 11, wherein the outer diameter of the balloon increasesby about 40% to about 400% of an uninflated outer diameter of theballoon within the working inflation pressure range of the balloon. 13.The device of claim 1, wherein the balloon is formed of a polymericmaterial selected from the group consisting of polyurethane elastomers,silicone polyurethanes, segmented polyamide block copolymers, segmentedpolyester block copolymers, styrene butadiene rubber, and radiationcrosslinked polyolefinic elastomers.